Recently, decentralised (on-blockchain) platforms have emerged to complement centralised (off-blockchain) platforms for the implementation of automated, digital ("smart") contracts. However, neither alternative can individually satisfy the requirements of a large class of applications. On-blockchain platforms suffer from scalability, performance, transaction costs and other limitations. Off-blockchain platforms are afflicted by drawbacks due to their dependence on single trusted third parties. We argue that in several application areas, hybrid platforms composed from the integration of on-and off-blockchain platforms are more able to support smart contracts that deliver the desired quality of service (QoS). Hybrid architectures are largely unexplored. To help cover the gap, in this paper we discuss the implementation of smart contracts on hybrid architectures. As a proof of concept, we show how a smart contract can be split and executed partially on an off-blockchain contract compliance checker and partially on the Rinkeby Ethereum network. To test the solution, we expose it to sequences of contractual operations generated mechanically by a contract validator tool.

In this paper we discuss how conventional business contracts can be converted into smart contracts-their electronic equivalents that can be used to systematically monitor and enforce contractual rights, obligations and prohibitions at run time. We explain that emerging blockchain technology is certainly a promising platform for implementing smart contracts but argue that there is a large class of applications, where blockchain is inadequate due to performance, scalability, and consistency requirements, and also due to language expressiveness and cost issues that are hard to solve. We explain that in some situations a centralised approach that does not rely on blockchain is a better alternative due to its simplicity, scalability, and performance. We suggest that in applications where decentralisation and transparency are essential, developers can advantageously combine the two approaches into hybrid solutions where some operations are enforced by enforcers deployed on-blockchains and the rest by enforcers deployed on trusted third parties.

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Converting a conventional contract into an electronic equivalent that can be executed and enforced by computers is a challenging task. The difficulties are caused by the ambiguities that the original human-oriented text is likely to contain. The conversion process involves the conversion of the original text into mathematical notation. In this paper we discuss how standard conventional contracts can be described by means of Finite State Machines (FSMs). This mathematical description helps eliminate ambiguities from the original text before the contract is coded into a computer program. The paper describes how to map the rights and obligations extracted from the clauses of the contract into the states, transition and output functions, and input and output symbols of a FSM. The FSM guarantees that the clauses stipulated in the contract are observed when the program that implements the contract is executed. Also, the paper suggests a middleware service required for the enactment of the contract represented as a FSM. Keywords

The services offered by Internet Data Centers involve the provision of storage, bandwidth and computational resources. A common business model is to charge consumers on a pay-per-use basis where they periodically pay for the resources they have consumed (as opposed to a fixed charge for service provision). The pay-per-use model raises the question of how to measure resource consumption. Currently, a widely used accounting mechanism is provider-side accounting where the provider unilaterally measures the consumer's resource consumption and presents the latter with a bill. A serious limitation of this approach is that it does not offer the consumer sufficient means of performing reasonableness checks to verify that the provider is not accidentally or maliciously overcharging. To address the problem the paper develops bilateral accounting models where both consumer and provider independently measure resource consumption, verify the equity of the accounting process and try to resolve potential conflicts emerging from the independently produced results. The paper discusses the technical issues involved in bilateral accounting.